1. Field of the Invention
The present invention relates to a method and a device for providing a supply voltage using generator units connected in parallel, for example, for a motor vehicle.
2. Description of Related Art
It is already known to supply power to the on-board electrical system of a motor vehicle using a generator.
In addition, it is already known to use at least two generators to supply energy to the onboard electrical system of certain vehicles, for example security vehicles, rescue vehicles, and utility vehicles, in order to ensure that the power requirements and/or the reliability requirements of the electrical supply are met.
The wear, and thus also the life span, of a generator are a function of several factors. One of these factors is the electrical utilization of the generator. The greater the electrical utilization of a generator, the greater is its wear, and the shorter its remaining life span. It is therefore desirable, in devices for providing the voltage supply to the consumers of a vehicle electrical system using a plurality of generators, to ensure that the degree of utilization of the generators used is the same.
In German patent document DE 10 2005 12 270.1, a method and a device are described for providing the supply voltage for the consumers of a vehicle electrical system using a plurality of generators. A control unit having at least one power transistor is allocated to each of the generators. In order to bring the degree of utilization of the generators into agreement, in one of the control units a pulse-width-modulated control signal, or a control signal derived therefrom that describes the pulse-duty factor of the pulse-width-modulated signal, is formed and is supplied to the power transistors of all the control units.
In addition, from published German patent document DE 41 08 861 a device is known having generators connected in parallel. In this known device, a voltage controller is allocated to each of the generators. In addition, the known device has at least one battery of which one terminal is capable of being connected to the voltage controller via an ignition switch. In addition, a charge control device is provided that is connected to the ignition switch and to the voltage regulators, and that is capable of being connected via a switching device to the negative terminal of the battery, which is preferably connected to ground. Between the charge control device, the voltage controllers, and the named switching device, there is situated a circuit system having a plurality of components that conduct in one direction and that block in one direction. This known device is intended to achieve the effect that through the use of two generators a high electrical power can be produced, and that using a single display device, for example a charge control lamp, errors that occur in one of the two generator-voltage controller systems can be signaled, while the other generator-voltage controller system can continue to operate without problems.